<html>
  <link rel="stylesheet" href="seamless-iframe.css">
  <body>
    <iframe src="/slow?100" id="frame" class="seamless"></iframe>
    <script>
      let frame = document.getElementById("frame");
      let doc = frame.contentDocument;
      doc.open();
      doc.write("<html>Rewritten. <img src=pixel.png> </html>");
      doc.close();
    </script>
  </body>
</html>
